The integration of a fingerprint sensor in a display panel is very desirable for the mobile fingerprint sensing industry. A conventional approach to address this challenge has been to integrate a fingerprint sensor in a common display panel such as an LCD panel or an OLED panel. In this approach, the priority is given to display properties and visual quality. Therefore, the final desired product is a display panel which is capable of detecting a fingerprint.
In a display having fingerprint sensing capabilities, the pixels in the display are also acting as capacitive sensing elements. A touch display is often based on TFT-technology implemented in ITO, making the circuitry essentially transparent. However, the TFT-technology is limiting in that a display typically comprises 1-6 transistors per pixel, whereas a fingerprint sensor typically requires significantly more transistors, which is difficult to achieve for a TFT display.
Accordingly, circuitry for high resolution capacitive fingerprint sensing can not easily be implemented in TFT technology. In particular, for sensing under glass, a higher sensitivity of the fingerprint sensor is required due to the increased distance between the finger and the sensor, which in turn requires additional circuitry.
Accordingly, there is a need for an improved fingerprint sensing device having integrated display functionality.